Not all the money i withdrew come out

I went to the ATM and withdrew money . and i never count the money because i'm always scared that someone behind me is watching me . so an ATM experience is me taking the money and leaving immediately. When i got home and counted the money i only had 500 instead of 600 that i withdrew . and this is not the first time my money was short , I thought i was staying with people who had sticky fingers . what should i do? count the money next time or what ?